The Science of Breathalyzers, and Why Some People Refuse to Take One

Posted by William Bly | May 19, 2015 | 0 Comments

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We're all familiar with the basic premise that while it's not illegal to drink and drive, perhaps it's just not a good idea. You're probably familiar with the fact that alcohol can have a negative impact on your basic motor skills, affecting depth perception, judgment, and movement. Any of these can make driving a car more risky, both for the driver and for others on the road. Because of the increased danger that comes from drinking and driving, the state of Maine, like all other states in the U.S., has passed laws to penalize those that are caught operating a vehicle under the influence of drugs or alcohol (OUI).

There's one problem with OUI laws: Not only do some people get drunk quicker than others, but everyone shows different signs of drunkenness or impairment. How do you effectively determine who's too drunk or impaired to drive?

Scientifically, alcohol is neither completely digested in your body, nor changed in the bloodstream – as your blood flows through your body, the alcohol level increases as the alcohol is absorbed into the blood stream via the walls of the small intestine and into the capillaries. The amount of alcohol in your blood is called your blood alcohol content (BAC), and is measured in milliliters of alcohol per 100 milliliters of blood. However, determining how much alcohol is in your blood during a traffic stop is difficult, as it would involve taking a blood sample. The thought of having a police officer taking a blood draw can make many people queasy.

There is, however, another way of determining how much alcohol is in your blood. When your blood flows through your lungs, some of the alcohol stays there. This happens at a steady rate – the same amount of alcohol is in 2,100 milliliters of breath as in 1 milliliters of blood. Therefore, when you exhale, the amount of alcohol on your breath can be used to show how much is in your blood. Using this fact, police officers rely on breathalyzers to determine your BAC.

For law enforcement, the use of breathalyzers is game-changing. They allow police officers to get scientific evidence of your BAC, without having to resort to something as intrusive as a blood draw. The value of this kind of evidence really shows itself if the OUI case goes to trial: Without having a BAC number, prosecutors are put in a position where they have to rely on the officer's rendition of how drunk a driver looked. Often, this does not have the same kind of impact on a jury that a BAC count does. Juries likely think that outward signs of drunkenness, like slurred speech or unsteady balance, are not perfect indicators of inebriation, while BAC is much more reliable. Ironically, this is not the case – BAC numbers are only general predictions of whether someone was drunk, or not. Other factors, like gender and weight, can affect a person's BAC, taking them over the legal limit when they're still sober.

Now, with all that being said, Maine no longer employs a blood alcohol standard when using a breath test. That means the Government doesn't have to show that the amount of alcohol on your breath equates to the same amount of alcohol in your blood. Instead, the Government only has to show what your breath alcohol content was at the time of driving, which is commonly referred to as BrAC. Theoretically, this makes it easier for the prosecution to obtain guilty verdicts as it eliminates argument about breath partition ratio and variability in a person's blood hematocrit levels and other scientifically based arguments that good OUI attorneys have relied on over the years.

Breath testing devices are scientifically problematic as they are notoriously unreliable. You need an experienced OUI attorney that can review your case and determine if the breath test was accurate. If you have any questions and are looking to speak with an experienced OUI attorney, call William T. Bly at (207) 571-8146.

About the Author

William Bly

William T. Bly, Esq. is a graduate of Rutgers College where he majored in Political Science with a minor in U.S. History. Attorney Bly attended and graduated the University of Maine School of Law. During his time in law school, Attorney Bly focused on criminal defense.

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